Transition Metal Hollow Nanocages as Promising Cathodes for the Long-Term Cyclability of Li-O2 Batteries

As a step towards efficient and cost-effective electrocatalytic cathodes for Li-O-2 batteries, highly porous hausmannite-type Mn3O4 hollow nanocages (MOHNs) of a large diameter of -250 nm and a high surface area of 90.65 m(2).g(-1) were synthesized and their physicochemical and electrochemical properties were studied in addition to their formation mechanism. A facile approach using carbon spheres as the template and MnCl2 as the precursor was adopted to suit the purpose. The MOHNs/Ketjenblack cathode-based Li-O-2 battery demonstrated an improved cyclability of 50 discharge-charge cycles at a specific current of 400 mA.g(-1) and a specific capacity of 600 mAh.g(-1). In contrast, the Ketjenblack cathode-based one can sustain only 15 cycles under the same electrolytic system comprised of 1 M LiTFSI/TEGDME. It is surmised that the unique hollow nanocage morphology of MOHNs is responsible for the high electrochemical performance. The hollow nanocages were a result of the aggregation of crystalline nanoparticles of 25-35 nm size, and the mesoscopic pores between the nanoparticles gave rise to a loosely mesoporous structure for accommodating the volume change in the MOHNs/Ketjenblack cathode during electrocatalytic reactions. The improved cyclic stability is mainly due to the faster mass transport of the O-2 through the mesoscopic pores. This work is comparable to the state-of-the-art experimentations on cathodes for Li-O-2 batteries that focus on the use of non-precious transition materials.